The phenomenon of "virgin births" has been observed in sharks and reptiles living in captivity, but scientists had never seen it happen in the wild among vertebrates. Fascinating new research shows sawfish living in a Florida estuary have the ability to have offspring through asexual reproduction.
A team of researchers determined about 3 percent of the estuary's sawfish were likely the products of asexual reproduction, also known a parthenogenesis, Stony Brook University reported. This is the first evidence of this type of wild birth among vertebrate animals. The smalltooth sawfish (Pristis pectinata) is considered critically endangered due to overfishing and the loss of coastal habitats, so the fact that they can asexually reproduce is especially significant.
"We were conducting routine DNA fingerprinting of the sawfish found in this area in order to see if relatives were often reproducing with relatives because of their small population size," said the study's lead author, Andrew Fields, a Ph.D. candidate at the Stony Brook University's School of Marine and Atmospheric Science. "What the DNA fingerprints told us was altogether more surprising; female sawfish are sometimes reproducing without even mating."
Parthenogenesis is common in invertebrates but not so much in vertebrates, and is believed to be triggered by an unfertilized egg absorbing a "sister cell" that is almost genetically identical to the egg itself. These offspring only have half the genetic diversity as its mother, making them more vulnerable to malformation and early death.
"There was a general feeling that vertebrate parthenogenesis was a curiosity that didn't usually lead to viable offspring," said Gregg Poulakis of the Florida Fish and Wildlife Conservation Commission, who led field collections of the sawfish. "The seven parthenogens we found looked to be in perfect health and were normal size for their age. This suggests parthenogenesis is not a reproductive dead end, assuming they grow to maturity and reproduce."
The researchers suggested these sawfish are so rare that females may fail to find a mate often enough to trigger a parthenogenetic process.
"It is possible that parthenogenesis is most often expressed in wild vertebrates when the population is at very low levels and the animals have difficulty finding one another," Fields said. "Parthenogenesis could help endangered species like sawfish dodge extinction for a little while, but it should also serve as a wake up call that we need serious global efforts to save these animals."
The findings were published in a recent edtition of the journal Current Biology.